Spin impurities in solid state spin systems, such as nitrogen-vacancy (NV) centers in diamond, have attracted considerable interest because their electronic spin degrees of freedom can be coherently controlled by microwave radiation, and the spin states of the system can be polarized and readout by optical fields. Long coherence times also make them appealing.
Spin impurities such as NV centers thus have wide applications, ranging from magnetometry, quantum computers and bioimaging to super-resolution microscopy. Obtaining good quality of signals for these applications, for example, increasing magnetic sensitivity for magnetometry, requires long spin coherence times and high photon collection efficiencies.
The traditional method for reading out the electronic spin state of the NV centers is fluorescence-based detection. However, only a small fraction of the fluorescence falls within the solid angle collected by the objective, so that the collected photons at the detector, in general, is less than 1%.
Accordingly, there is a need for more sensitive methods and systems for detecting electronic spin states of spin impurities such as NV centers in diamond.